Spin and Orbital Moments and Magnetic Order in Fe3O4 Nanoparticle Assemblies

Spin and Orbital Moments and Magnetic Order in Fe3O4 Nanoparticle Assemblies Yanping Cai Department of Physics and Astronomy Master of Science Fe3O4 magnetic nanoparticles of 5 to 11 nm in size were prepared by organic methods. Particle size was analyzed by both X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques. Zero Field Cooling (ZFC) / Field Cooling (FC) and magnetization loop measurements were recorded by VSM, and they confirmed superparamagnetic behavior in the sample. The blocking temperature is found to be in the range of 30 K ⇠ 170 K. It has a dependence on the particle size. ZFC / FC curves also indicate the presence of magnetic coupling between particles. X-ray Magnetic Circular Dichroism (XMCD) measurements of these nanoparticles were measured at 80 K and 300 K. By using the sum rules, spin and orbital magnetic moments were calculated from the XMCD signal. The results confirm a quenching orbital moment and a large spin moment. The calculated total magnetic moments are somewhat smaller than in bulk Fe3O4. Also, the spin moment at 80 K was found to be larger than at 300 K. X-ray Resonant Magnetic Scattering (XRMS) measurements at different temperatures, polarizations and fields were carried out. The intensity profile gives information on the interparticle distance between nanoparticles which is in consistent with TEM results. A magnetic signal was extracted by calculating the dichoric term, when the energy is tuned to resonant edges. This magnetic signal is confirmed by comparing the dichroic terms at different conditions.